In embedded control systems of today, developments in digital technology have enabled complex functionality. However as a direct result from the development, the need of additional system capacity provided by software and various components such as sensors, processors, display units, data buses and memory units is increasing.
Apart from implementing more functionality and interconnectivity in control systems, using less Space Weight and Power (SWaP) and a reduced number of cabling are further important drivers. Updates of embedded hardware and software during a products life span make adaptability and modularity another interesting design parameter. Other incentives include achieving cost efficient development, production and maintenance, where one possible route is to implement Commercial of the Shelf (COTS) technology instead of expensive specialized technology.
Real-time systems for safety critical control applications, wherein typically data from sensor/s are acquired, communicated and processed to provide a control signal to an actuator pose strict demands regarding bandwidth, data delivery time, redundancy, and integrity. Failure to meet one or several of these demands can in applications including “brake-by-wire” or “steer-by-wire” prove dangerous.
One such area wherein reliable high-speed real-time execution and communication of data is applicable is within avionics systems. Advances in technology during late 1960 and early 1970 made it necessary to share information between different avionics subsystems in order to reduce the number of functional modules such as Line Replaceable Units (LRU:s). A single sensor such as a position sensor provided information to weapon systems, display system, autopilot and navigation system.
The high level architecture of avionics systems has gone from federated meaning separate LRU:s for separate functions to integrated modular avionics (IMA) meaning several functions integrated into multifunctional LRU:s. The connectivity allowing communication between different LRU:s has gone from low bandwidth point-to-point connections to higher bandwidth bus connections.
Guidance set out by Radio Technical Commission for Aeronautics (RTCA) in DO-178B and RTCA DO-254 regulates how to design and develop software and respective hardware in a safe way in order to show airworthiness, according to a criticality scale. However certification and subsequent recertification of software according to the DO-178B represents a substantial cost of developing software based avionic control systems.
In order to assist development of modern control systems for avionics a set of guidance documents such as DO-297 and Aeronautical Radio Inc. (ARINC) 651 defines general concepts for IMA systems. Further ARINC 653 “Avionics application software standard interface”, defines an Application Program Interface API referred to as Application Executive (APEX), implemented in Real-Time Operating Systems (RTOS) used for avionic control systems. APEX allows for space and time partitioning that may be used wherever multiple applications need to share a single processor and memory resource, in order to guarantee that one application cannot bring down another in the event of application failure.
Document U.S. Pat. No. 6,886,024 B1 discloses a system in which execution of plural applications distributed over plural computers is controlled using a simplified script language to realize coordination among plural applications to enable facilitated construction of upper-order distributed applications. Each computer includes, on an agent platform, an agent base capable of having a shell agent, a local service agent and an application agent, an agent movement unit, thread generating unit, remote control unit and agent generating unit. A script language input through an input unit is interpreted by the shell agent to boot the application agent. The application agent supervises an actual application. The shell agent and the application agent can be moved to another computer using the agent movement unit and can have communication with an agent in the other computer with the aid of the remote control unit.
Document WO/2001/086442 A2 discloses techniques for inter-application communication and handling of I/O devices in an Integrated Modular Avionics (IMA) system enable the integration of multiple applications while maintaining strong spatial and temporal partitioning between application software modules or partitioned applications. The integration of application modules is simplified by abstracting the desired application interactions in a manner similar to device access. Such abstraction facilitates the integration of previously developed applications as well as new applications.
However, moving from specialized avionic systems using dedicated hardware and software in attempts to achieve increased system performance, modularity and cost efficiency tends to produce complex systems with decreased determinism.
Accordingly, there is a need in the art of avionics to present an improved avionics system, intended to enhance dependability and determinism.